1. Field of the Invention
This invention relates generally to magnetic recording and/or reproducing apparatus, such as, video tape recording and reproducing apparatus (VTR), and more particularly is directed to improvements in such apparatus having a still motion reproducing mode of operation during which the video signals corresponding to a selected frame or field are repeatedly reproduced.
2. Description of the Prior Art
Existing video tape recording and reproducing apparatus generally comprise a tape guide drum having one or more rotary magnetic heads associated therewith to record or reproduce video signals on a magnetic tape which is usually wound on supply and take-up reels with the tape between such reels being wrapped helically about at least a portion of the circumferential surface of the drum and being driven, during recording and normal reproducing operations, by a cooperating capstan and pinch roller and by suitable rotation of the take-up reel. Thus, during recording operation, the rotary heads record the video signals in successive parallel record tracks that extend obliquely across the tape at an angle to the longitudinal direction of the latter determined by the helical path of the tape on the guide drum, the rotational speed of the heads and the speed at which the tape is longitudinally driven by the capstan. During such recording operation, the rotation speed of the rotary heads is usually selected so that a field of video signal information will be recorded in each record track. During normal reproducing operation, the rotary speed of the heads and the speed at which the capstan drives the tape are the same as for the recording operation so that the rotary heads can accurately span the successive oblique record tracks and reproduce the successive fields of video signal information recorded therein.
When still motion reproducing operation of the described apparatus is desired, the longitudinal movement of the tape is halted, for example, by moving the pinch roller away from the capstan, so that the rotary heads will repeatedly scan along a track which extends obliquely across the tape at an angle determined only by the helical path of the tape on the guide drum and, hence, which is inclined relative to the oblique record tracks. Thus, depending upon the random position of the tape in which the longitudinal movement thereof has been halted, the track along which the rotary heads scan the stationary tape may be disposed relative to the record tracks on the tape anywhere between a first position in which the scanning track intersects a record track adjacent the middle of the latter and deviates from such record track at the opposite ends thereof, and a second position in which the ends of the scanning track intersect two adjacent record tracks at the opposite ends of the latter and the middle portion of the scanning track extends across the guard band or spacing between the two adjacent record tracks. In either case, the video signals repeatedly reproduced during a still motion reproducing operation will contain so-called guard band noises which produce characteristic disturbances in the video picture obtained when the reproduced video signals are displayed by a monitor or the like. However, if the tape is halted with the scanning track of the rotary heads in the above described second position relative to the record tracks on the tape, the disturbance due to the guard band noises will extend horizontally across the center of the picture or image displayed on the monitor screen and thus be most disruptive. On the other hand, if the scanning track of the rotary heads is in the above described first position relative to the record tracks on the tape, the disturbances due to the guard band noises will extend across the top and bottom of the displayed picture where they are least conspicuous and interfere as little as possible with viewing of such picture.
In existing video tape recording and reproducing apparatus of the open-reel type, that is, in which the supply and take-up reels are readily accessible during operation of the apparatus, it has been the practice, after longitudinal movement of the tape has been halted for a still motion reproducing operation, to manually turn either the supply reel or the take-up reel for adjusting the position of the stationary tape relative to the scanning track of the rotary heads until the disturbances due to guard band noises occupy the positions in which they are least conspicuous, as indicated above. However, such adjustment of the position of the tape by direct manipulation of the supply or take-up reel is troublesome even in the case of an open-reel type apparatus, and is impossible in the case where the supply and take-up reels are contained in a cassette housing and, therefore, are not accessible for such manipulation.